This invention relates generally to seals and, more particularly, to a method of applying a thin film polymer coating on an elastomeric seal for enhanced wear resistance and improved environmental resistance; and to the resulting seal.
Construction equipment operates in the most severe conditions imaginable, from the extreme cold of the arctic to the extreme heat of the equator. Seals used in such equipment must be effective in those conditions; plus be able to live in abrasive conditions, such as a track seal for a track-type tractor; or immersed in or exposed to hydraulic fluid, such as in a hydraulic system of a hydraulic excavator. Some seals are utilized in static applications while others are in dynamic applications. Some seals are face-type seals and others are sliding seals. Elastomeric seals are used in many of these applications and are subject to degradation in service by several mechanisms. In some cases, degradation involves abrasive wear while in others it involves oxidation or swelling in hydraulic fluids.
Elastomeric seals are used in a variety of applications, which demand resilience and resistance to high temperatures and corrosive attack. Elastomeric seals may be used in equipment, such as pumps, engines, mixers, compressors, valves, etc. When used in hydraulic systems, leaks are an anathema and superior reliability is required. In instrument applications micro-contamination is often unacceptable and seals must possess superior resistance to degradation and corrosion.
The requirements for a suitable seal are many. For example, it must not degrade or lose its elasticity in contact with the fluids being handled, even at extreme temperatures and pressures. The seal must not allow these fluids to pass through easily by permeation. Furthermore, the material must not swell appreciably in contact with the fluids being handled, even at elevated temperatures. For example, if an O-ring in contact with a moving surface swells appreciably, it may be extruded into a close-clearance area where it will be torn by friction. When an O-ring swells while in contact with a fluid under pressure or high temperature, and the pressure or temperature is then reduced, the O-ring may shrink from its extruded position in a way that causes fluid leakage to occur.
Elastomers are subject to degradation in service by several mechanisms. Most elastomeric seal failures are caused by thermal aging and fluid attack. Swelling may cause elastomeric seals to expand out of their retaining grooves, thereby causing leaks in a system. Generally, higher temperatures increase the deteriorative effect of chemicals on polymers. Thermal aging, including temperatures caused by peak loading conditions of equipment may cause elastomers to become hard and brittle, decreasing the ability of seals to conform to irregular surfaces. In addition, there is evidence that the presence of oxygen may deteriorate some elastomers subjected to temperatures greater than 200xc2x0 F. In some cases, degradation of elastomers involves abrasive wear, while in others it may involve oxidation or swelling in hydraulic fluids.
It has been common practice in industry that, when various items are potentially damaged by vapors within the local environment, some form of coating is applied to reduce the potential interaction. Typically, various organic coatings are applied; one commonly utilized coating being a parylene. Other similar organics, such as polymers, are also utilized. Another form of protective coating utilized in industry is a metal or ceramix layer; typically aluminum being the metal utilized.
Although these coatings have been generally satisfactory, long-term exposure to detrimental constituents often results in damaging of the coated item. This is particularly the case when the item is relatively easily attacked by corrosion, etc. The exact nature of the penetration of the coating by the damaging constituent is not always known; however, in the case of metal coatings, the metal tends to have pinholes in the layer as a result of the deposition techniques that are utilized for its application. Similarly, diffusion and/or small pinholes often penetrate the organic layers.
We are aware of the following U.S. Pat. Nos.:
It is a general object of the present invention to provide a product having enhanced wear resistance and/or improved environmental resistance.
Another object is to provide a seal where the elastomer has improved resistance to degradation.
A further object of the present invention is to improve the resistance of elastomers to degradation through the application of thin film polymer coatings to the elastomers by plasma polymerization or through plasma etching of the elastomers. The thin film polymer coating significantly retards the arrival of deleterious media at the surface of the elastomer and reduces their effects to an acceptable level.
A still further object is to improve the wear resistance of products.
In accordance with the present invention there is provided a product having improved resistance and comprising a substrate which may be formed from an elastomeric material or a metal and having a surface, and a thin polymer film plasma polymerized and deposited onto the substrate, thereby forming a product having improved resistance.
In accordance with another feature of the present invention there is provided a method for improving the resistance of a product comprising the steps of depositing a plasma polymerized film onto the surface of its substrate by applying an electric field to a low pressure gas, causing collisions between atoms and free electrons to form excited species, impinging the excited species upon the surface of the substrate exposed to the low pressure gas, and reacting the excited species with other excited species and with monomers to adhere a polymer film on the surface of the substrate; etching the plasma polymerized film on the surface of the substrate to improve the resistance of the film; and thereby forming a product with improved resistance.
Plasma polymerization is an efficient process that advantageously allows polymer synthesis and deposition to be combined. Furthermore, plasma polymerized films are advantageously adherent to the substrates upon which they are formed. Plasma polymerized films also advantageously have properties which can be tailored for specific applications. Moreover, a wide range of monomers can be plasma polymerized, unlike the traditional methods for polymerization, whose applicability is limited to a narrower range of monomers.
These and other objects of the invention will be apparent on review of the drawing and the Best Mode for Carrying out the Invention.